With the track cycling done and dusted the two-wheel program is shifting gears and bringing in the sport's brash younger cousin - BMX.

Bicycle Motocross has only been putting the 'X' into the Olympics since 2008, but it makes a bold statement.

Six-thousand fans were blasted by music that ranged from American rockers Linkin Park to dubstep's Skrillex, while competitors launched into their time trial to decide the seedings for the racing rounds.

US rider Brooke Crain also planted herself into the concrete after going over the front of her handlebars on the final straight.

"I've had my fair share of those crashes and things happen as well and it's just part of what happens in any sport you go to there is injuries, things happen, and part of what we do is taking spills here and there and thankfully I think she is going to be all right with that one," Crain's team-mate Alise Post said.

The same set of jumps brought down Latvian Edzus Treimanis to audible grounds from the crowd. With blood trickling down his face he wheeled his somehow intact bike back to the pits.

Many are lucky just to be in London and competing.

South Africa's Sifiso Nhlapo broke his neck in 2009 and following rehabilitation returned to the sport to place second in the 2010 world championships.

He has also broken his jaw, been in a coma and last year tore his anterior crucial ligament in his left knee.

"Again I was out for six months on the couch," Nhlapo said.

"It's been a real struggle but really happy I'm here. At the high level everyone can give you a story about injuries."

Team GB's medal hope is one Liam Phillips.

But he almost did not make the Games. He broke his collarbone just over 10 weeks ago and has been told he risks a repeat injury.

"I know that if I crash then the chances of that collarbone breaking again is likely to happen," Phillips said.

"But it's the Olympics in your home country what are you going to do?"

The crowd is obviously as unashamedly parochial as the one in the Velodrome, which has been clocked at 114 decibels - or like standing next to a power saw.

Phillips says he can hear their screams of support over the music and through his full face crash helmet.

"I've been reading and seeing everybody's interviews after competition and sort of laughing really saying it can't be that big a deal but God I sure believe now," he said.

Post says it will be a bigger factor than the 440-metre course.

"The track today was awesome, obviously in my first practice session it was a bit harder," she said.

"Obviously the conditions are going to be a big factor and dealing with the atmosphere. Those are going to be the bigger obstacles on this track than the actual track itself."

Australia has strong medal hopes in the form of debutants Caroline Buchanan, the fastest female qualifier, and world champion Sam Willoughby, who qualified sixth.

But he will be facing defending Olympic champion Maris Strombergs of Latvia in the quarter final.

"A lot of young kids have stepped up and made it to the Olympic Games and they are very good right now, on top of the game," Strombergs said.

The top four in each men's quarter-final will progress to the semi-final and then likewise to decide Friday's finals line-up. The 16 women will be split into two semis with the top four into the final.

So they may, in theory, only need to win one race to claim gold. But judging by BMX's history it will be a tough one.

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